Uplink power control using received reference signal

ABSTRACT

A method for determining uplink power level, implemented in a base station, comprises receiving a communication signal over an uplink common control channel. The interference on the uplink common control channel in response to the received communication signal is measured and a channel quality of the uplink common control channel is monitored. A quality margin for the communication signal is provided and transmitted over a downlink control channel.

CROSS REFERENCE TO RELATED APPLICATIONS

This application a continuation of application Ser. No. 10/857,156,filed on May 28, 2004, which is a continuation of application Ser. No.10/124,030, filed on Apr. 17, 2002, now U.S. Pat. No. 6,745,045, whichis a continuation of application Ser. No. 10/100,383, filed on Mar. 18,2002, now U.S. Pat. No. 6,587,697 and which claims priority from U.S.Provisional Application No. 60/290,730, filed on May 14, 2001, all ofwhich are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to wireless digital communication systems.More particularly, the present invention is directed to a code divisionmultiple access (CDMA) communication system utilizing uplink powercontrol for adaptive modulation and coding.

BACKGROUND

CDMA third generation (3G) cellular telecommunication systems applyadaptive modulation and coding (AM&C) to transmissions to achieve andimprove radio resource utilization and provide increased data rates foruser services. AM&C techniques take into account RF propagationconditions in advance of transmissions in order to determine modulationand coding rates that will take greatest advantage of current RFpropagation conditions.

One method for determining RF propagation conditions is to perform aphysical channel quality measurement at the receiver in advance of eachtransmission. This measurement is sent to the transmitter, which thendetermines the appropriate modulation and coding rate for the particulartransmission based upon the physical channel quality measurement.

RF propagation conditions can change rapidly, particularly for mobileapplications. Since the quality measurement of the radio interface isused to determine the appropriate modulation and coding, and since thechannel quality measurement can change rapidly due to the changing RFpropagation conditions, the performance of the adaptive transmissionprocess is directly related to the time period (i.e. latency) betweenwhen a quality measurement is performed and when that transmission isinitiated. Therefore, for optimal AM&C, it is necessary to performchannel quality measurements with minimal latency for all users withactive data transmissions.

Physical or logical control channels are used to transfer channelquality measurements from a receiver to a transmitter. Channel qualitysignaling may utilize either dedicated control channels to each userequipment (UE) or common control channels shared by all UEs. Whendedicated control channels are used, a continuous signaling channel isavailable over time for propagation of channel quality measurements foreach UE. In terms of performance, this is an optimal solution for AM&Csince the quality measurement is continuously available. Transmissionscan occur at any time, taking into account the continuously availablequality measurement for appropriate modulation and coding settings.Additionally, with a dedicated control channel always available in theuplink, the channel can be also used to support low rate uplink datatransmissions.

The difficulty with the dedicated control channel approach is thatphysical resources are continuously allocated even when there is no datato transmit. A primary application of AM&C techniques are non-real timehigh data rate services, for example, Internet access. For these classesof service, the best quality of service (QoS) is achieved with short,high rate transmissions with relatively long idle periods between eachtransmission. These long idle periods result in an inefficient use ofdedicated resources.

The problem can be minimized with pre-configured periodic dedicatedchannel allocations. But this results in periodic unavailability ofquality measurements. If the quality measurements are not continuouslyavailable, for UEs which have transmissions at any one point in time,only some portion of the UEs will have recent channel qualitymeasurements.

When common control channels are used, a continuous signaling channel isshared by all UEs within a cell. In Third Generation-Time DivisionDuplex (3G TDD) systems, the uplink common control channel typicallyoccupies a single time slot out of multiple time slots. Procedures aredefined for each UE's access to the common control channel and UEidentities may be used to distinguish UE specific transactions.

To avoid contention-based access to the uplink common control channel,individual allocations are required to be signaled on the downlinkcommon control channel. Alternatively, some mapping between the downlinkallocation and uplink allocation may be defined. Each UE then accessesthe uplink common control channel in accordance with its allocation.Since uplink transmissions cannot always be predicted by the network,and since uplink transmissions are infrequent, (in some applicationstransmitting only 5% of the time), periodic allocations of the uplinkcommon control channel are also necessary for propagating uplink radioresource requests to support uplink user data. Additionally, when commoncontrol channels are used for AM&C operation, no inner loop powercontrol mechanism exists for each UE, since the common control channelsare not continuously available.

What is needed is an efficient method of performing power control whileminimizing the overhead necessary to perform such a method. Powercontrol will minimize the interference introduced by the uplink commoncontrol channel.

SUMMARY

A method for determining uplink power level, implemented in a basestation is disclosed. The method includes receiving a communicationsignal over an uplink common control channel. The interference on theuplink common control channel in response to the received communicationsignal is measured and a channel quality of the uplink common controlchannel is monitored. A quality margin for the communication signal isprovided and transmitted over a downlink control channel.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1A is a simplified block diagram of a base station of the presentinvention.

FIG. 1B is a simplified block diagram of a user equipment of the presentinvention.

FIG. 1C is a simplified block diagram of an alternative embodiment of abase station of the present invention.

FIG. 2 is a simplified block diagram illustrating one preferredembodiment of the process of the common control channel uplink powercontrol of the present invention.

FIG. 3 is a flow diagram showing an alternative embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The present invention will be described with reference to the drawingfigures wherein like numerals represent like elements throughout.

FIG. 1A is a simplified block diagram of a universal mobiletelecommunications system terrestrial radio access network (UTRAN) basestation 12, (hereinafter BS 12), which communicates wirelessly over anRF link 25 to a UE 30, (shown in FIG. 1B). The UE 30 may be a wirelesscell phone, PDA or other like device which may include additionalcapabilities such as paging, e-mail and the like.

The BS 12 comprises an antenna 24, (or multiple antennas), anisolator/switch 22 (or like device), a time slot interferencemeasurement device 26, an uplink common control channel receiver 28, acommon control channel quality monitoring device 18, a summing device 20and a reference downlink channel spreading and modulation device 14. TheBS 12 receives communications over the radio link 25 via the antenna 24.Received signals are coupled to the interference measurement device 26and the uplink common control channel receiver 28 through theisolator/switch 22.

The interference measurement device 26 measures time slot interferenceon the uplink common control channel. For example, the interferencemeasurement device 26 may measure interference signal code power (ISCP).The interference measurement device 26 provides an output (Icc), whichis an indicator of the amount of interference on the uplink commoncontrol channel.

The receiver 28, which may be a matched filter, RAKE or like device,receives and applies the signal in the uplink common control channel tothe channel quality (CQ) measuring device 18 for monitoring the channelquality (CQ) of the uplink common control channel and providing aquality margin (QM) for a given UE.

The QM can be signaled, for example, as a calculated Signal toInterference Ratio target (SIRtarget) that the UE transmissions areexpected to achieve. The QM can also be based upon a combination offactors including the SIRtarget, RF propagation conditions and/or theQoS requirements for the service desired by the UE. In turn, theSIRtarget may be based upon measurements from previous transmission fromthe particular UE, such as the block error rate (BLER). Unlike theuplink interference level, the QM is not required for each individualuplink common control allocation and can, as one option, be separatelyspecified by the BS 12 or even eliminated, as shown in FIG. 1C.

Referring back to 1A, when not specified by the BS 12 or when notconstantly updated by the UE 30, the QM may be stored and the mostrecent QM is used.

The Icc and QM values are applied to first and second inputs of thesumming device 20. The output of the summing device 20 is input to thespreading modulation device 14. Although, the QM and the Icc may becombined by the summing device 20 as shown, they may also be encodedinto a single parameter, further reducing downlink signaling overhead.As further alternative, the Icc may be signaled separately, for example,on a broadcast channel. In that case, only the QM will need to besignaled. The Icc and QM, if not combined or encoded into a singleparameter, may be separately input into the spreading and modulationdevice 14 and sent over separate downlink channels. The output from thespreading and modulation device 14 is passed to the antenna 24 throughthe isolator/switch 22 for transmission to the UE 30. The QM and Icc aresignaled over one or more downlink control channels. The path lossmeasurement, (which is performed by the UE 30 as will be explained infurther detail hereinafter), is performed on the reference channel.

As shown, FIGS. 1A-1C refer to reference channels (and controlchannel(s)). It should be noted that the present invention comprisesonly a portion of the signaling that is performed between the base 12and the UE 30. It is not central to the present invention whether themeasurements described herein are sent over a single reference channel,a single control channel or multiple reference and/or control channels.It is contemplated that a combination of reference and/or controlchannels may be used within the spirit and scope of the presentinvention.

Referring to FIG. 1B, the UE 30 comprises an antenna 32, anisolator/switch 34, a reference channel receiver 36, a path losscalculation device 42, power level calculation device 44, an adaptivemodulation and coding controller 46, a signaling receiver 48, a poweramplifier 50. The antenna 32 receives communications from the BS 12 overthe RF link 25 and applies the communications through theisolation/switch 34, as appropriate to either the reference channelreceiver 36 (i.e., the reference channel(s)), or the signaling receiver48 (i.e., the control channel(s)).

The reference channel receiver 36, receives and processes one or morereference channels in a manner that is well known to those of skill inthe art. Accordingly, such detail will not be included herein. Thereference channel receiver 36 performs an estimate of the referencechannel for data detection and provides the power level of the receivedsignal to the path loss calculation device 42. The path loss calculationdevice 42 employs the power level to determine power loss in thedownlink transmission.

The QM and Icc information transmitted by the BS 12 are received by thesignaling receiver 48, which passes this information to the power levelcalculation device 44. The power level calculation device 44 uses theoutputs of the path loss calculation device 42 and the signalingreceiver 48 to determine a proper power level for transmission to BS 12as a function of path loss and interference in the RF link 25.

The output 44 a of the power level calculation device 44 regulates theoutput power of the UE 10 via control of the power amplifier 50. Thepower amplifier 50 amplifies, as appropriate.

The output of the amplifier 50 is transmitted to the BS 12 through theisolator/switch 34 and the antenna 32.

As those of skill in the art would understand, TDD utilizes atransmission structure whereby a frame is repetitively transmitted, eachframe comprising a plurality of time slots. Data to be transmitted issegmented, and the segmented data is then scheduled for transmission inone or more time slots. For TDD, the CQ interference measurement fromthe same slot in a previous frame is very valuable in determining themodulation and coding rate of the current frame. As will be described ingreater detail hereinafter, the CQ interference measurement as measuredat the base station is signaled in the downlink in advance of the commoncontrol uplink transmission.

One embodiment of the method 10 of the present invention is shown in theflow diagram of FIG. 2. In this method, at the BS 12, at step S1, thereference channel is transmitted, with a power level known to the UE 30.The UE 30 continuously calculates path loss at step S2. The BS 12continuously measures uplink interference on all time slots, at step S3,based on transmissions from the UEs, (only one UE 30 being shown in FIG.2 for simplicity); and can also be based upon transmissions from otherbase stations, (only one BS 12 shown for simplicity).

The BS 12, at step S4, determines the need for an uplink common controlchannel; for example 1) an AM&C measurement report; or 2)Hybrid-Automatic Repeat Request (H-ARQ) control information. Thisdetermination may optionally be in response to the receipt of a datablock. At step S5, the BS 12 allocates a specific uplink common controlchannel, indicating the uplink interference level Icc in that time slot.The BS 12 at step S6 signals the uplink common control channel to beutilized and the uplink interference level (Icc) for the allocatedchannel. These parameters are signaled over a downlink control channel.Note that the parameters of the specific uplink control channel may beimplicitly known.

The UE 30, at step S7, determines the appropriate uplink power level fortransmission to the BS 12 based upon the current path loss measured bythe UE 30 at step S2 and the interference level Icc obtained from the BS12.

As stated hereinbefore, in an alternative embodiment the QM may also besignaled along with, or separate from, the interference level Icc. Thisalternative embodiment of the method 20 of the present invention isshown in FIG. 3, providing further optimization of the uplink commoncontrol channel power level. Those steps in FIG. 3 that are numbered thesame as FIG. 2 implement the same steps of the procedure. However,further optimization is achieved by additionally signaling a requestedQM with the uplink common control channel allocation. The QM is based,among other aspects, upon previous transmissions from the particular UEreceived at step S3. FIG. 3 shows step S6 modified as step S6A and stepS7 modified as step S7A. As shown in both FIGS. 2 and 3, the BS 12 mayperform step S4 in response to receiving a data block; or may beindependent of whether or not a data block is received.

Referring back to FIG. 2, the transmit power level of a UE (Tue) may berepresented by the following equation:Tue=PL+Icc  Equation (1)where PL is the path loss; and Icc is the interference level for anuplink common control channel communication. The path loss (PL) may becalculated as follows:PL=Tref−Rue  Equation (2)where Tref is the power of the reference signal at the BS 12 and Rue isthe received power at the UE 30 of the reference signal.

The UE 30 at step S8, initiates an uplink common control transmission atthe uplink transmit power level calculated using Equations 1 and 2; thetransmission being received by the BS 12, at step S9.

When the QM is transmitted from the BS 12 to the UE 30 as shown in thealternative method 20 of FIG. 3, the transmit power level of a UE (Tue)may be represented by the following equation:TUE=PL+QM+Icc  Equation (3)where PL is the path loss; QM is the desired quality margin and Icc isthe interference level for the uplink common control channelcommunication. The path loss (PL) may be calculated as follows:PL=Tref−Rue  Equation (4)Where Tref is the power of the reference signal at the BS 12 and Rue isthe received power of the reference signal at the UE.

The present invention has several advantages over prior art methods. Themeasured uplink interference level can be specified in the allocationmessage, assuring a very low latency uplink interference measurement isavailable to the UE. Alternatively, the measured uplink interferencelevel can be provided via the downlink common control channel or othermeans. Since the AM&C uplink control channel is expected to exist in asingle 3G TDD mode timeslot, still further efficiencies are perceived.Normally, in slotted systems employing similar open loop power controlmechanisms, interference must be reported for each slot for properoperation. Since only one slot is used for the uplink common controlchannel and therefore only the uplink interference for one slot has tobe signaled, minimal overhead is introduced to the downlink allocationsignaling for the benefit of more efficient use of uplink radioresources.

While the present invention has been described in terms of the preferredembodiment, other variations which are within the scope of the inventionas outlined in the claims below will be apparent to those skilled in theart.

What is claimed is:
 1. A method for determining uplink power level,implemented in a base station, comprising: receiving a firstcommunication signal over an uplink channel from a user equipment (UE);measuring a channel quality of the uplink channel in response to thereceived first communication signal; providing a quality margin derivedfrom the first communication signal; determining that the UE is to sendan adaptive modulation and coding report to the base station;transmitting an allocation of an uplink channel and the quality marginover a downlink control channel to the UE in response to the determiningthat the UE is to send an adaptive modulation and coding report; andreceiving a second communication from the UE in at least one time slotin the allocated uplink channel in response to the allocation of theuplink channel and the quality margin; wherein the second communicationincludes an adaptive modulation and coding report and a transmissionpower level derived from the quality margin.
 2. The method of claim 1,further comprising combining the measured interference and the qualitymargin.
 3. The method of claim 2, further comprising encoding themeasured interference and quality margin into a single parameter.
 4. Themethod of claim 1, further comprising transmitting the measuredinterference over a broadcast channel.
 5. A base station, comprising:circuitry configured to receive a first communication signal over anuplink channel from a user equipment (UE); circuitry configured tomeasure a channel quality of the uplink channel in response to thereceived first communication signal; circuitry configured to provide aquality margin derived from the first communication signal; circuitryconfigured to determine that the UE is to send an adaptive modulationand coding report to the base station; and circuitry configured totransmit an allocation of an uplink channel and the quality margin overa downlink control channel to the UE in response to the determining thatthe UE is to send an adaptive modulation and coding report; and whereinthe circuitry configured to receive the first communication is furtherconfigured to receive a second communication from the UE in at least onetime slot in the allocated uplink channel in response to the allocationof the uplink channel and the quality margin; wherein the secondcommunication includes an adaptive modulation and coding report and atransmission power level derived from the quality margin.